Steffi Graf required three stitches after husband Andre Agassi accidentally hit her in the face with his racket during a fundraising event in Houston.
Agassi and Graf have raised millions for charity
Graf and Agassi were holding hands - her left to his right - while rallying with a couple of youngsters when his follow-through struck her in the face.
Her cut lip was stitched by a doctor who had paid to play with the couple at the US Clay Court Championships.
Agassi said: "It was an unfortunate accident, but she's okay."
Agassi and Graf were in Texas as part of a US TV reality show called 'The Big Give,' an upcoming Oprah Winfrey production.
An auction benefiting an elementary school in the Houston vicinity chosen for the show raised at least $225,000 on Sunday.
Agassi retired last year at the US Open, having won eight Grand Slam titles.
His German wife retired in 1999 with 22 Grand Slam titles to her name. The couple has two children and live in Las Vegas.